Continuous one-piece prosthesis

ABSTRACT

A one-piece continuous polymeric prosthesis is disclosed and taught. The prosthesis is intended for patients with a below-knee amputation. The one-piece socket-pylon-keel allows good energy storage and release for a superior feel during physical activities. The construction and the materials makes for a much lighter weight prosthesis than conventional types.

This is a division of U.S. Pat. application Ser. No. 757,949, filed Sep.12, 1991, now U.S. Pat. No. 5,219,364.

BACKGROUND OF THE INVENTION

A goal of prosthetists has been to reduce the weight of below-kneeprostheses to reduce the energy and hence fatigue of the wearer.Reduction in weight, however, has to be balanced with the need tomaintain sufficient weight-bearing strength to support the wearer duringnormal activity levels. The various materials used in the priorprostheses, such as wood and alloy metals (e.g. titanium), also tendedto be rigid. This lack of material flexability did not allowsignificient energy storage and return during activities such as walkingor running which, in turn, detracted from a natural feel to the wearerof the prosthesis.

The most common artificial leg for below-knee (b.k.) amputees are of arigid nature. A solid shank will connect the socket, which mounts theartificial leg to the residual limb of the amputee, and the artificialfoot. The shank is often made out of a rigid alloy such as onecontaining titanium or is made from shaped wood. The attachment of theshank to the artificial foot is also usually rigid. While advances havebeen made in the construction of artificial feet to provideenergy-storing/releasing systems, these advances primarily have theenergy-storing system contained within the foot itself and not able tostore energy through the shank due to the termination of theenergy-storing system at the rigid foot-shank union. The energy-storingsystem can take the shape of a C-shaped plastic spring running from theankle through the arch and terminating toward the ball of the foot. Inthe case of the metal shanked artificial leg, the system can weigh inthe range of 31/2-4 pounds. In the case of the wood shank, theartificial leg can weigh on the order of 3 pounds.

The Flex-Foot® artificial leg produced by Flex-Foot, Inc., Irvine, Ca.,is an example of the currently available artificial leg which exhibits amore natural dynamic action by using a flexible energy storing pylon andkeel, the flexible pylon and keel is formed from-a strip of laminatedreinforced composite which is mechanically attached to the socketdescending down to form the pylon and continuing on to form the keel ofthe artificial leg. Applying pressure to the Flex-Foot® artificial leg(e.g. walking on it) causes flexation of the pylon and foot which actsas a spring to store energy and release it during walking or runningmovements. While the Flex-Foot® artificial leg allows for morenatural-feeling movement due to its energy storing and returning actionthan prior rigid artificial legs and while lighter than other prior artlegs made of titanium and/or wood, its weight (on the order ofapproximately 21/2 pounds) can be of concern to geriatric patients, aswell as more active patients.

For geriatric patients, artificial legs of these weight ranges can causediscomfort and reduced activity. Oftentimes small savings in weight canproduce great results due to the nature of walking with its repeatedactivities of lifting the leg. Likewise, for younger amputees, theincreased weight can cause increased fatigue during exercise and slowertimes when competing e.g. in races. The prior art also suffers from alack of flexibility which would allow sufficient energy storage andreturn to approximate the dynamics involved in athletic activities suchas running.

The invention provides a prosthesis with improved energy storage andreturn action. The invention also provides a prosthesis that issubstantially lighter than known prostheses while still offeringsufficient weight-bearing strength. The invention further provides aprosthesis that is readily capable of having its energy storage andflexation action modified. The invention provides a durable prosthesiswhich provides an energy storage and return action for the wearer. Theinvention provides a prosthesis which can be easily fabricated bytrained personnel using readily available orthopaedic materials andcommonly available equipment.

From the .subsequent detailed description taken in conjunction with theaccompanying drawings and subjoined claims, other objects and advantagesof the present invention will become apparent to those skilled in theart.

SUMMARY OF THE INVENTION

This invention is directed primarily to an artificial leg or prosthesisfor a below-knee amputee and is fabricated out of a continuous sheet ofplastic such as a polypropylene-polyethylene blend.

A test or trial prosthesis is fitted to the amputee to determine theproper sizing and fit of a socket as well as the relative orientation ofpoints such as the ball of the foot and heel of the foot to the terminusof the residual limb. A sole and heel cushion is selected to approximatethe outline of the natural foot. A keel mold is placed on the surface ofthe heel and sole cushion and is attached to a male model for the socketsized from the test or trial prosthesis to allow proper fit. The keelmold has an outline similar to that of the sole and heel cushion. Raisedribs extend from the ankle area of the keel mold. The keel mold isattached to the socket model by a steel mandrel. The model of the socketis aligned relative to the heel and sole cushion to replicate thealignment arrived at previously through use of a test prosthesis. Asheet of softened thermoplastic is molded over the entire assemblyforming a socket where molded over the model of the socket, a pylon weremolded over the steel mandrel, and a keel were molded over the keelmold. The raised ribs of the keel mold will form corresponding ridges ofplastic which are designed to stiffen the keel and/or the keel-pylontransition. Vacuum is applied to the inside of the wrapped sheet tovacuum form the plastic sheet to the mold surfaces.

After cooling, the keel mold, mandrel and model of the socket areremoved, the plastic edges of the prosthesis are then trimmed, and thesole and heel cushion attached to the underside of the keel. Theprosthesis may be further finished in the manner normally used for anendo-prosthesis, e.g., a cosmetic covering put on the outside. Theprosthesis is attached to the patient in the conventional manner by theinsertion of the residual limb into the socket and the placement of arubber cuff around both the socket and limb.

The resultant product is a one-piece continuous prosthesis, much lighterin weight than other known prostheses, weighing on the order of 20ounces or less. Even lighter artificial limbs can be constructed forgeriatric patients where the load-bearing requirements are not ascritical. Resulting prostheses also allow for an energy storage andreturn function during walking by controlled flexing of the keel incombination with the pylon. The pylon also allows limited flexure fromside to side or laterally, more closely mimicking the action of anatural limb below the knee. The pylon can be adjusted for footposition, eversion, inversion and rotation along with plantar ordorsi-flexation and pylon flexibility. The keel has an interchangeableheel wedge. The stiffness of the keel and/or pylon can also be adjustedby removal of material to reduce rigidity. Keel stiffness can beincreased by the addition of material such as a stiffening beam to thekeel. Keel and pylon stiffness can be increased by insertion of anadditional keel-pylon assembly. Reheating the plastic allows changes tobe made in the alignment of the prosthesis.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a test prosthesis mounted in a verticalalignment jig.

FIG. 2 is a perspective view of a mold of the invention mounted in avertical alignment jig.

FIG. 3 is a perspective view of a mold of the invention ready to haveplastic vacuum-thermoformed over it.

FIG. 4 is an exploded perspective view partially in section of aprosthesis in accordance with the present invention.

FIG. 5 is an exploded perspective view of an alternate embodiment of theinvention.

DETAILED DESCRIPTION INCLUDING PREFERRED EMBODIMENT

The preferred embodiment of the invention is a below-knee prosthesis. Atest or trial prosthesis is first fitted to the patient. The trialprosthesis may be of any conventional known design and is used primarilyto establish certain reference points for the definitive, i.e., final,prosthesis. Included in the reference points to be determined by thetrial prosthesis are the fit of the socket to the residual limb and thelocation and form of the distal foot. These fitting techniques areconventional techniques and commonly known to prosthetists for fittingof prostheses.

Referring to FIG. 1, once the fit and alignment of the trial prosthesis(10) has been finalized, it is placed in a vertical alignment jig (12)and a plaster impression is formed of the distal foot (14). The socket(16) is secured to the vertical alignment Jig (12) by collar (18). Theinside of the socket (16) of the trial prosthesis (10) is alginated toform a male mold by casting alginate (a casting product from COELaboratories, Inc., Chicago, Ilinois 60621) into the interior of thesocket (16) to form the alginate impression (20).

As shown in FIG. 2, the alginate impression (20) is locked intoalignment on the vertical alignment jig (12) using the pipe (22) of thejig to maintain alignment of the alginate impression (20) relative tothe plaster impression of the distal foot (14). The alginate impression(20) is then removed from the socket being careful to maintain thereference points which determine alignment. The alginate impression (20)is then splinted with plaster of paris bandages to form female socketmold (21) over the alginate impression (20). A buildup area (24) iscreated using the plaster bandages to allow the collar (18) on thevertical alignment jig (12) to secure and reference the plaster femalemold socket (21) on the jig (12). These referencing points in thebuildup area are preferably established at the patellar tendon level.

The collar (18) is then repositioned in the vertical alignment jig (10)and the plaster covered alginate impression (20) is locked into andreferenced to the vertical alignment jig (12) by the reference points inthe buildup area (24) of the female socket mold (21). The alginateimpression (20) and pipe (22) are now removed and the alignment of theremaining plaster female socket mold (21) is maintained solely by thereference points established by the interface of the collar (18) withthe buildup area (24).

A prosthetic sole and heel combination (26) is matched with and placedon the plaster impression of the distal foot (14). The preferred soleand heel combination prosthesis is manufactured by Otto Bock OrthopaedicIndustries, Inc., 3000 Xenuim Lane North, Minneapolis, Minnesota 55441.Depending on the manufacturer and size of the sole and heel combination,some modification may be needed when transferring from one sole and heelcombination prosthesis to another. It is important that the heel andball orientation of the sole and heel combination (26) should not bealtered from that established through fitting of the trial prosthesis tothe wearer and recorded in the plaster impression of the distal foot(14). Finishing technique of the resulting prosthesis can also vary thesize of the sole and heel combination (26) selected. As an example,cosmetic covers may add a full-size over the internal sole and heelcombination prosthesis.

A keel form (28) is then positioned onto the sole and heel combinationprosthesis (26). The keel form (28) will serve as a mold over which thekeel portion of the prosthesis will be formed. Therefore, the keel form(28) should be sized to match the outline of the sole and heelcombination (26) which is substantially the outline of a natural foot.The keel form (28) can also be selected to have a rib mold (30) so thatthe resultant prosthesis will have stiffening ribs cast into it. Theresultant ribs may be sized to strengthen the area where the keeltransitions into the pylon to resist fractures or failure at thatjuncture. The stiffening ribs will affect the stiffness of the resultantkeel and hence its energy storage and return properties. The weight andactivity level of the patient should be assessed in determining theproper stiffness of the resultant keel. While stiffness of the finalkeel and prosthesis as a whole can be modified as explained below,proper selection of a keel form with a sufficiently large rib mold (30)allows sufficient stiffness to be cast into the keel. The exactstiffness characteristic can be later modified as explained below byremoving material or, if necessary, adding material to the prosthesis.The rib mold should be sized so that the resultant rib would end at theapproximate location of the metatarsal heads in a natural foot. Byterminating the rib at the approximate location of the metatarsal heads,the keel is more likely to flex at that location, thus approximating theflexing characteristics of a natural foot.

The desired socket-pylon relationship is then established in both thesagittal plane and the coronal plane.

The socket-pylon intersection point (34) is translated to a spot on thedistal end of the plaster female socket mold (21) which will establishthe socket-pylon intersection point (34) marking the upper end of thepylon where it is integrated into the socket. A 3/4 inch vertical holeis then cut in the distal end of the plaster female socket mold (21) atthe socketpylon intersection point (34). A length of 3/4 inch metal pipeconstituting a mandrel (36) is secured to the keel form (28) at thepoint established for the lower end of the pylon at the keelpylonintersection point (32) and is inserted through the 3/4 inch hole in thedistal end of the plaster female socket mold extending approximately 2-3inches into the interior of the socket. The top end of the mandrelshould be flared or textured to provide adequate bonding strength of themandrel to the material which will be cast inside of the plaster femalesocket mold.

The thermoplastic material used to form the final prosthesis shrinks asit cools and allowance must be made for the dimensional change of thethermoplastic from its heated size to its cooled size. In addition, thekeel form (28) will be removed from the final prosthesis and allowancemust be made for the absence of its thickness when adhering the sole andheel combination (26) to the underside of the resultant keel. Therefore,the plaster socket should be raised relative to the mandrel by an amountsufficient to compensate for both the shrinkage of the thermoplasticmaterial and the absence of the keel form (28) in the final product.These two factors result in a 3/16-1/4 inch length discrepency along thevertical axis and the socket should be raised by this amount during thisstage of alignment transfer. The inside of the plaster female socketmold (21) is then coated with a mold release agent such as soap orsilicone oil. The plaster female socket mold is then filled with plasterto create the definitive socket male mold.

The junction of the mandrel (36) and keel form (28) should be securedand reinforced to eliminate eversion/inversion, dorsi-plantar flexion orrotational alignment deviation. In an effort to secure the pylon keeljunction, the mandrel-keel form junction is reinforced by a reinforcingband (38) formed by example from a composite of epoxy or polyester resinand fiberglass particles. Other methods of achieving the necessaryreinforcement can include mechanical or adhesive means to build up thearea of the mandrel-keel form junction (32). The result should provide amold surface for the resultant prosthesis which gives a generoustransition surface from the mandrel (36) to the proximal portion of thekeel form (28).

The resultant assembled model is removed from the vertical alignmentjig. The plaster female socket mold is removed, leaving the cast inplace plaster socket form attached to the mandrel. Care should be takento avoid impact or stress on the keel form which might deform ormisalign the keel form. The article is then smoothed to remove anysurface irregularities and/or sharp edges which may be replicated in thefinal article.

Referring to FIG. 3, a truncated cone (39) is fashioned around themandrel (36) and male socket mold (41) intersection to provide asmoothly transitioned mold surface. The truncated cone is preferablyfabricated from Pelite®. Pelite® is a registered trademark ofDurr-Fillauer Medical, Inc., P.O. Box 1678, Chattanooga, Tennessee37401. Similar material can be substituted.

A mold release agent should then be applied to the assembled model tofacilitate removal of the model from the fabricated final prosthesis. Inthe preferred embodiment, a nylon stocking or stockinette (40) is pulledover the entire assembled mold (42) and knotted off at the top as seenin FIG. 3. The nylon stocking reduces sticking of the material to themodel as well as maintaining air passageway between the prosthesisforming plastic and the model during vacuum forming as discussed below.Where the nylon stocking (40) does not conform to the assembled modelsurface, such as transition points from the keel form to the mandreland/or the mandrel to the socket, the nylon can be tied down with finethread (41). The assembled model (42), encased in the nylon stocking(40), is then horizontally mounted to a jig (44) operably connected to avacuum source (46).

A sheet of the plastic material (48) for the final prosthesis is thencut to proper size to allow fitting over and encasing the entireassembled model (42). The preferred material for fabricating theprosthesis is a thermoplastic copolymer consisting of polypropylene andpolyethylene. The most preferred material is a copolymer sheetconsisting of 95 percent polypropylene and 5 percent polyethylene suchas sold by Maramed Precision Corp., 2480 West 82nd Street, Hialeah,Florida 33016. The thickness of the polymer sheet is to be determined bythe strength desired in the ultimate article. This, in turn, dependsupon the weight and activity level of the patient. It has been foundthat 1/4 inch thick sheet material has been suitable for moderately tohighly active patients. Less active patients and/or patents of reducedweight can have successful results with a prosthesis formed from thinnermaterials. Such patients can also benefit from the further reduction ofweight obtained from using thinner materials.

The copolymer sheet (48) is then heated in an oven to 330°-355° F. Careshould be taken so that the sheet (48) is not overheated and loses theintegrity of the copolymer mix. The assembled model is horizontallysecured in the jig (44) with the toe portion of the keel form pointingup. The sheet of heated copolymer is draped over the top of thehorizontal assembled model and then pressed to conform to the assembledmodel. Care should be taken to have thickness of the sheet remainuniform, i.e., not thinned due to stretching. This is especiallyimportant in the segment formed over the mandrel (36) which becomes thepylon. The edges of the copolymer sheet are brought together along theback of the assembled model and pressed together to form a flanged seamalong the posterior portion of the assembled model. A vacuum is thenapplied by the vacuum source (46) between the copolymer sheet (48) andthe assembled model (42) to more closely conform the copolymer sheet tothe assembled model in a vacuum-forming procedure. It has been foundthat the nylon stocking (40) functions to maintain air passages alongthe surface of the assembled model. These air passages reduce the chanceof bubbles forming in the final prosthesis by pockets of air trappedbetween the copolymer sheet (48) and the assembled model.

Additional reinforcement means such as a stiffening beam (51) (shown inFIG. 4) can be added to the keel form to stiffen the front portion ofthe resultant keel and create a stiffer toe lever. One method ofincreasing the stiffnesses is to mount additional polymeric materialonto the keel form so that it is fused to the polymer sheet when it iswrapped around the assembled model. It has been found that ahorseshoe-shaped piece of copolymer made from the same material as thatof the final prosthesis can be placed on the keel form with the openends of the horseshoe placed approximately one inch anterior to themetatarsal heads. This additional material will considerably increasethe stiffness of the toe lever when it is encased in the finalprosthesis. Additional reinforcing means can include spring steel orcarbon graphite composites encased in the polymer addition to formsprings or stiffeners in the keel.

Once the copolymer has cooled, the assembled model encased in plastic isremoved from the fixture. The plaster male model around which the sockethas been formed is broken out and removed. The mandrel and keel form arealso removed, as is the nylon stocking. Referring to FIG. 4, theresultant prosthesis (50) is a one-piece polymeric prosthesis with theadditional stiffening beam (51) being secured thereto. The edge of thesocket is then trimmed to remove excess material and burrs or sharpedges. The posterior flange seam (52) is also trimmed. Care should beused so as not to remove the entire posterior flange seam as the flangeportion performs a stiffening function and reduces flexibility of thepylon in the anterior or posterior direction. Additional material fromthe flange can be removed to increase flexibility. The keel rim (54),the material depending downward from the border of the keel, i.e., thematerial that is formed over the sides of the keel form, should betrimmed, but some material depending downward should be left intact. Thekeel rim increases the rigidity of the keel and serves to position andsecure the sole and heel combination prosthesis (26).

A plug (62) is inserted into the pylon in the ankle area. The plug maybe made of clay and should be positioned above the area corresponding tothe natural ankle as at (56). Approximately 30 grams of material thatforms a rigid foam such as IPOS R-120 rigid foam from IPOS NorthAmerica, Inc., P.O. Box 320, Niagra Falls, NY 14304, is prepared andpoured into the inverted ankle cavity. The heel and sole combinationprosthesis (26) is placed over the reacting foam. The bolt hole (58) ofthe heel and sole combination prosthesis is used to vent excess foam asthe mixture reacts. A funnel may be placed through the bolt hole (58) tovent excess foam during reaction. The resultant foam bonds itself to thecombination sole and heel prosthesis (26) while remaining relativelyunbonded to the copolymer sheet. The combination sole and heelprosthesis with the attached rigid foam can now be removed. The nowrigid foam has formed a mast (60) which aids in securing the combinationsole and heel prosthesis to the heel and pylon. The plug (62) isremoved. The mast may be coated with nylon stockinette to help eliminaterubbing noise. The mast as attached to the combination sole and heelprosthesis is inserted into the bottom of the keel. A 1/8 inch hole (63)is drilled through prosthesis (50) and the mast (60) through theanterior portion of the ankle. A mechanical fastener (64) such as a pinor screw is secured through the hole (63) holding the mast and hence thesole in place. The 3/4 inch circular hole in the distal end of thesocket left by the removal of the mandrel is also plugged such as byPelite®.

The prosthesis may be further finished in a manner normally used forendoskeletal prostheses. The cosmetic cover as sold by the Flex-Foot®Company has been found to work successfully. Care should be taken sothat the combination sole and heel prosthesis has been properly sized toallow the cover to be fitted.

The resultant prosthesis (50) is much lighter than conventionalbelow-knee prostheses and is particularly useful for geriatric wearers,especially those with reduced strength. The prosthesis is free fromstructural material other than the copolymer material itself. A typicalprosthesis of the present invention sized for an adult male of vigorousactivity is on the order of less than 20 ounces. The reduced weightgives less resistance to movement, allowing the wearer to maintainactivity for longer periods of time.

The resultant prosthesis is also useful for vigorous amputees who findthat the energy-storing and releasing action of the keel (71) integratedwith the pylon (60) which itself is integrated with the socket (61) hasa more natural feel during running and walking. The keel can flex,especially in the region of the metatarsal heads, giving a more naturalflexion akin to a natural foot. The ability of the keel to flex alongvarious lines combined with its footprint approximating the natural footadds to its stabilizing characteristics. The keel is also able to storeenergy while flexing. The flexing of the pylon also serves an energystorage and return function during walking or running. The pylon canstore energy along its inter length in part due to its integration withthe socket as one piece. The keel and pylon can cooperatively flex dueto their continuous nature. The pylon and keel can also flex laterallyduring activity more closely approximating the flexing of the naturalankle. The vigorous amputee also benefits from the lighter weight,especially in competitive events.

Should alignment correction or realignment be necessary, the pylonsection (66) of the prosthesis may be aligned by reheating. Ifrotational corrections are necessary, the 3/4 inch mandrel isreinserted. A 3/4 inch solid rubber mandrel may be inserted to makepositional alignment changes. The rubber mandrel will prevent collapseor deforming of the pylon cylindrical cross-section as changes are madeto the heated prosthesis pylon. Care should be exercised to maintain thecylindrical cross-sectional shape of the pylon during alignment changes.

Referring to FIG. 5, a further feature of the present invention is theuse of a sport pylon (68) providing for modification of the dynamics ofthe prosthesis. The sport pylon is a secondary pylon and keel assemblyparticularly useful for vigorous amputees. The sport pylon is sized tofit within the interior of the pylon (66) of the prosthesis (50) withthe keel portion (70) of the sport pylon fitting within the keel (71) ofthe prosthesis. After removing the combination sole and heel prosthesis(26) and mast (60), insertion of the sport pylon alters the dynamics ofthe prosthesis by providing a second spring layer in the keel section.This may be useful for providing more energy storage in, for example,the toe section. The sport pylon also stiffens the pylon (66) of theprosthesis (50) to reduce flexing. The sport pylon can also be formed sothat the portion of the keel corresponding to the natural toe is plantarflexed. The sport pylon should have its own combination sole and heelprosthesis (26) dedicated to its use to insure proper height of thetotal prosthesis. The hardness of the heel dedicated to the sport pyloncan differ from the heel normally used with the prosthesis depending onthe activity the sport pylon is intended for. As an example, thehardness of the heel can be changed usually by increasing its hardness.The position and outline of the sole and heel combination of the sportpylon can also be altered from the sole and heel combination used withthe prosthesis. The activities that the sport pylon is intended for mayalso call for no heel wedge of the sole and heel prosthesis (26) to beused. Amputees participating in sprinting events may prefer this, asthere is very little heel strike in such activity. The sport pylonallows the amputee to wear his prosthesis throughout the day at acomfortable walking alignment with a soft heel and flexible keel-pyloncombination. Upon arriving at the court, track, or ballfield, the sportpylon may be inserted to alter the dynamics of the prosthesis for a morerealistic energy-returning sensation from the ball of the foot and toeswhen running or jumping.

EXAMPLE

A 28-year-old male patient weighing approximately 175 pounds and with avigorous activity level had been fitted with a laminate/endo/Seattlefoot prosthesis for his medium length below-knee amputation. The subjectwas very active, participating in running, sprinting, and playingvolleyball, among other sports. The subject was fitted with a prosthesisof the present invention. The complete prosthesis weighed approximately11/4 pounds (20 ounces). Over the first three to four days, theprosthesis was broken in for a slight reduction in the toe lever orstiffness of the toe portion of the keel. The prosthesis is reinforcedover the forefoot with a second layer of 1/4 inch copolymer sheet in theform of a horseshoe. As a result of the initial break-in, the toe hasexhibited an upward migration of a minimal amount and the prosthesis asa whole shows no adverse reaction to the weight and activity level ofthe subject. The subject has previously worn "energy-storing"feet andmore conventional types of foot such as the SAFE (Stationary AttachmentFlexible Endoskeletal), SACH (Solid Ankle Cushioned Heel), andGreissenger feet. The subject describes action of the keel and pylondynamics as a mid-point between a Seattle® foot and a Flex-Foot®.

While the above detailed description describes preferred embodiments ofthe present invention, it will be understood that the present inventionis susceptible to modification, variation and alteration withoutdeviating from the scope and fair meaning of the subjoined claims.

What is claimed is:
 1. A method of forming a prosthesis for a below-kneeamputee comprising:providing a model of the residual limb providing akeel mold to form a keel; connecting said residual limb model with saidkeel mold with a pylon mandrel in an aligned relation to form anassembled prosthetic model; forming a single polymeric sheet over saidassembled prosthetic model; removing said assembled prosthetic model;and forming a continuous prosthesis having a hollow pylon portion, akeel portion having a substantially planar platform with a top andbottom surface which are substantially parallel to one another and aheel and toe, and a limb receiving portion.
 2. The method of claim 1further comprising securing resilient sole means to the portion formedover said keel mold.
 3. The method of claim 1 further comprisingremoving polymeric material after forming to modify the stiffness of theresultant prosthesis.
 4. The method of claim 1 wherein said forming stepfurther comprises thermo-vacuum forming said polymeric sheet to saidassembled prosthetic model.
 5. The method of claim 3 further comprisingattaching keel stiffening means to increase the resistance to flexing ofthe area formed by the keel mold.
 6. The method of claim 1 furthercomprising attaching a stiffening beam to the surface formed by saidkeel mold to provide selectively removable material for adjusting theflexation of said surface formed by said keel mold.
 7. The articleformed by the method of claim 1 wherein the alignment of said keel tosaid socket is capable of modification after initial formation.
 8. Themethod of forming a prosthesis comprising,proving a model of a trialprosthesis fitted to a wearer; thermo-vacuum forming a single sheet ofsubstantially homogeneous copolymer material over said model to producea continuous one-piece prosthesis; removing said model from the formedprosthesis; forming a continuous prosthesis having a hollow pylonportion, a keel portion having a substantially planar platform with atop and bottom surface which are substantially parallel to one anotherand a heel and toe, and a limb receiving portion; and selectivelyremoving copolymer material to adjust the stiffness of the prosthesis.9. The prosthesis formed by the method of claim 8 wherein saidprosthesis is substantially free of structural material non-homogeneousto the copolymer.